On Feb 24, 12:34*pm, "Jon" wrote:
I'm trying to wire a transfer circuit for a generator.

The generator will be located in the barn. *The electrical service is at the
house. *Two 120vac wires and a ground go to the barn. *There is *one* unused
wire from the house to the barn I can use for a signal circuit.

When the power goes off at the house, I need to disconnect the service to
prevent backfeed and activate for generator power to both the house and the
barn. *When the service power goes on I need to disconnect the generator to
avoid damaging it and restore normal service to the house and the barn.

I have,

*one 240vac 60 amp dpdt mercury relay
*two 120vac 60 amp 3pdt relays.

Any ideas?

Jon Giffen

Answer: Ask your insurance company if they will buy you a new house
(and barn) if (for any or no reason) the thing catches fire.

You need a listed mechanical switch, not a relay.
You can buy automatic transfer switches, of course - which are a form
of motorized mechanical switches.

As for control wiring to an automatic transfer switch, these are
typically low-voltage, but not always.
Although, most ATS I've seen will sample the utiliity and switch by
themselves, and the control wiring is mostly for cycle-timers and
testing, stuff like that.

If I understand where you're going....
NO. You can not use an extra (unused) wire in the bundle that already
carries the two 120 VAC.
The control wiring is separate. Can't even be in the same conduit.

Of course, check your local codes -- one obvious exception is that the
local Inspector probably has the ability to "approve" anything, but I
wouldn't hold my breath.
Way too much liability.

Go get yourself a real switch, designed for this purpose. Manual or
Automatic.
They cost much less than your house, or yours or someone else's life!

Also, I hope your "extra" wire is not the neutral.
If so, ask yourself what happens if the neutral to your house lifts.
Also, (totally different issue), remember that the Utility and your
generator will not be synchronized.
So, if you attempt an instaneous switchover, at some point, you'll be
high on the AC cycle from the utility, and low on the genertor -- or
vice versa.
This causes maximum current to flow for a split second, and will
probably nuisance-trip the breakers.
You can by phase monitors, but for residential use, a simple time
delay between switch activations should do the trick.
Generator - disconnect (wait) - then switch back to utility.
Easy.

Also, come to think of it, you probably want a safequard to your
generator is not connected until it reaches the proper output and
waveform.


-mpm